First, terms used herein are described below. In this description, sodium niobate (general formula: NaNbO3) is hereinafter referred to as NN. Further, NN is originally an orthorhombic, but is regarded as a pseudo-cubic for the sake of simplicity of expression. Unless otherwise specified, a crystal orientation, a crystal plane, an orientation, and an X-ray diffraction index of NN are described in pseudo-cubic notation. A solid solution of NN and barium titanate (general formula: BaTiO3) and a solid solution of NN and potassium niobate (general formula: KNbO3) each adopt any one of monoclinic, orthorhombic, cubic, and tetragonal crystal systems, or simultaneously adopt a plurality of these crystal systems depending on compositions. For the sake of simplicity of expression, however, the solid solution of NN and barium titanate, the solid solution of NN and potassium niobate, and other perovskite-type materials are also discussed as pseudo-cubics as is the case with NN unless otherwise specified.
It has been known in recent years that an NN-containing oxide such as the solid solution of NN and barium titanate or the solid solution of NN and potassium niobate is a promising lead-free piezoelectric material having a low environmental impact. Further, in general, piezoelectric performance of a piezoelectric ceramics can be improved by controlling crystal orientation.
According to Non Patent Literature 1, a plate-like NN particle is produced by a topochemical micro-crystal conversion (hereinafter, referred to as TMC) method. Then, an oriented ceramics containing NN as a component is produced by a doctor blade method using a slurry containing the plate-like NN particle.
Patent Literature 1 discloses a method of producing a plate-like particle by a technique other than the TMC method. A solid state reaction is employed to produce a cuboidal particle in which an A site of NN is partially substituted with Li, K, or the like and a B site thereof is partially substituted with Ta or the like, and a plate-like particle is then produced by a doctor blade method using a slurry containing the cuboidal particle.
As a method of producing a cuboidal NN particle by a technique other than a solid state reactionstate reaction, Patent Literature 2 discloses that a cuboidal NN particle can be synthesized by a solvothermal method.